To provide a method of treating garbage, which exhibits high-level organic decomposition performances to secure the primary fermentation of the garbage.

The method comprises a series of the following steps: an agitation step wherein garbage and previously decomposed garbage are agitated by feeding them into a rotating rotary treatment tank, and heating and air blowing are applied to the mixture to adjust the fed garbage to a water content and a temperature suited for the organic decomposition fermentation; a fermentation step wherein after the heating and the air blowing are stopped, the treatment tank is slowly rotated, oxygen is fed into the tank, and the mixture is adjusted to a pH suited for the organic decomposition fermentation of the fed garbage; and a drying step wherein after the feed of oxygen is stopped, the treatment tank is rotated at a rotation speed higher than that in the agitation step, and the mixture is dried to a suitable water content under heating and air blowing.